The external review committee on pure reference materials at the National Analytical Reference Laboratory

Abstract

The preceding paper described the implementation of a quality assurance system suitable for accreditation to ISO Guide 34 by the Pure Substance Reference Material (PSRM) team of the National Analytical Reference Laboratory (NARL). One of the key components of this system has been the establishment of an external advisory committee that scrutinises each candidate material that is to be offered as a reference material. At the time of writing 190 reference materials were available from NARL, including a range of illicit drugs and agricultural chemicals in addition to anabolic steroids and their metabolites, and all have been reviewed by the external committee prior to final approval by the accredited production signatory.

Synthesis and Characterisation of reference materials

The members of the pure reference material group have a strong background in synthetic and analytical organic chemistry. They, and AGAL, have a range of analytical methods at their disposal. Some candidate reference materials are obtained from commercial or other sources. However the majority are either prepared internally or their production is sub-contracted to a small number of experienced laboratories which have a demonstrated competency in the synthesis of high purity organic compounds. Table 1 gives examples of the types of compound investigated on a typical agenda for a committee meeting.

Table 1. List of synthesised compounds assessed at a meeting of the external review committee in April 2000

Techniques routinely used to characterise reference materials are given in Table 2. Major issues that arise in assigning purity are the quantification of the various classes of potential impurities. These can include small levels of organic compounds of related structure, retained solvent and moisture, and (rarely) non-volatile inorganic contaminants. In the case of isotopically-labelled materials the extent of enrichment also needs to be quantified. In addition the qualitative identity of the material needs to be demonstrated unambiguously, in particular in terms of the regio- and stereochemistry of what are at times complex molecular structures possessing a number of functional groups. All the techniques in Table 2 are used on most of the compounds, and all must give consistent and unambiguous results.

Table 2. Methods used to assess the identity and purity of reference materials

Accreditation and the role of the external review committee

The NARL Pure Substance Reference Materials laboratory [1] was the first laboratory in the world to gain accreditation to ISO Guide 34. The original terms of accreditation were for the: "Production of certified reference materials and reference materials of pure substance organic solids at room temperature for agrochemicals and agrochemical metabolites, steroids, steroid metabolites and deuterates, and illicit drugs."

The existence of an external review committee in an oversight role was commented on favourably both by the accreditation assessment team and by a CCQM Peer Review of the activities of NARL undertaken in 2001.

The review committee consists of three external people. The professor of analytical chemistry at the University of New South Wales (DBH), chairs the committee and provides expertise in metrology in chemistry. A professor of organic chemistry from one of the major universities in Sydney oversees aspects of synthesis and organic analysis. At present he is Professor David Black from the University of New South Wales. The third member represents a major user of reference materials, Dr Ray Kazlauskas, who heads the Australian Sports Drug Testing Laboratory. Members of the pure substance reference material laboratory attend committee meetings. The head of the section (SW), provides secretarial assistance, prepares paperwork and determines the frequency of meetings. The committee has independence to ask for explanations of data put before them, request further evidence of identity, or address any matters which it thinks relevant. Although the committee is advisory and has no statutory powers, no reference material has been released until the committee has been entirely satisfied.

Papers are sent out before each meeting detailing the compounds to be scrutinised, and with information about synthesis and characterisation. Most spectra and chromatograms are included, together with the proposed certificate that will go to purchasers of that reference material. A number of actions on members of the laboratory usually result from a meeting. Typically further characterisation, or re-running of spectra are required on a minority of the materials. Actions taken must be reported back to a subsequent meeting before a material is recommended for release. As an example the action taken following concern of the purity of 16β-Hydrofurazabol is given below (extract from the minutes of the meeting of 4^th April 2000).

"Further analysis of 16β-Hydrofurazabol (Compound 7) was carried out following the last meeting to determine if the second species evident in both proton and carbon NMR spectra of this compound is an impurity or a conformational isomer. Further analysis, coupled with the GC data showing the compound to be pure, and published references postulating the existence of conformational isomers for furazabol, suggests that a confomer, rather than an isomer or other impurity, is present. For customers, the known purity will be provided, and the data is also provided, which states confomers rather than impurities are present."

NARL believes that the existence and absolute independence of the review committee is essential to maintain credibility in the program. Having experts who scrutinize the output of the laboratory at the most basic level is important. The members of the laboratory who synthesize and characterize the reference materials have useful interaction with the experts, and have come to understand some of the metrological issues involved with reference material production.

Current issues

At present there is a discussion within the committee as to the most appropriate way to quote and certify purity. For materials that will be used as references for identity, traceable values of purity are not essential. However if reference materials are to be used to calibrate quantitative methods, for example in the course of registering agrochemicals or in determining the amount of illicit drug present in a police or customs seizure, then demonstration of metrological traceability is necessary to certify the material. The extent to which the percentage area of a GC-FID or HPLC chromatogram, coupled with supporting evidence showing the absence of solvent or non-volatile residues, can be used to determine a purity with a stated uncertainty is a matter of ongoing debate and technical investigation [2].

Arising from the accreditation reassessment in November 2001, investigation of the traceability of the amount of substance provided when materials are supplied as nominal small (typically 1 mg) solid aliquots in sealed ampoules was made a condition of ongoing accreditation. Studies to address this concern were undertaken and the results and conclusions obtained were reviewed and commented on by the committee prior to the reply of the section to the accreditation body.